Servo pattern for skew based tape dimensional stability compensation

ABSTRACT

In response to a rotation of timing-based servo (TBS) patterns of a first servo band and a second servo band, heights of top and bottom portions of servo stripes of servo frames of the TBS patterns are adjusted to compensate for changes in a usable height of the servo stripes caused by the rotation.

BACKGROUND

The disclosure relates to tape storage systems, and more specificallyrelate to a servo pattern for skew based tape dimensional stabilitycompensation.

In magnetic media, data is typically stored as magnetic transitions,e.g., data is magnetically recorded on a surface of the magnetic media.The data stored is typically arranged in data tracks. A typical magneticstorage medium, such as a magnetic tape, includes a plurality of datatracks. Transducer (read/write) heads are positioned relative to thedata tracks to read/write data along the tracks. Accordingly, a tapedrive head locates each data track and accurately follows the path ofthe data track. To achieve this, servo techniques have been developedwhich allow for a precise positioning of the head relative to the datatracks. One such technique makes use of servo patterns, that is,patterns of signals or recorded marks on the medium, which are trackedby the head. The servo patterns are recorded on the tape in order toprovide a position reference for the data tracks. In other words, aservo head reads a servo pattern, which is then interpreted by a servocontroller into a position error signal (PES). The PES is then used toadjust the distance of the servo head relative to the servo pattern andensure a proper positioning of the transducers with respect to the setof data tracks.

In a magnetic tape medium, the servo patterns are stored on dedicatedtracks (called servo bands). A plurality of patterns may be definedwithin a servo band and a plurality of servo bands may be relied upon byprocesses that read and write data on a tape. The data tracks arearranged between the servo bands. A particular servo technique uses atiming-based servo (TBS) pattern, which makes use of non-parallel marks,to which time or distance variables may be associated. In TBS systems,recorded servo patterns include transitions with two different azimuthalslopes. An estimate of the head lateral position is derived from therelative timing of pulses generated by a servo reader reading the servopattern. In a TBS format, the servo patterns are prerecorded in severalbands distributed across the tape, where the bands on which the servopatterns are prerecorded are referred to as servo bands. Data isrecorded in data tracks in the regions located between pairs of servobands.

Tape Dimensional Stability (TDS) is a measure of the positionalstability of the data tracks relative to each other and is a function ofthe tape properties and environmental effects such as temperature,humidity, tension, creep, etc. These environmental factors may cause thetape to expand or contract laterally, across the width of the tape.Therefore, when a tape is written to in one environmental condition andsubsequently read from in another environmental condition, the positionof the data tracks across the tape width may change enough to causesignal degradation or read errors.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, a tape formatting device, a computer programproduct, a tape, and a servo write head in which in response to arotation of timing-based servo (TBS) patterns of a first servo band anda second servo band, heights of top and bottom portions of servo stripesof servo frames of the TBS patterns are adjusted to compensate forchanges in a usable height of the servo stripes caused by the rotation.

In certain additional embodiments the TBS patterns are adjusted tocompensate for an angular displacement between equivalent servo framesof the first servo band and the second servo band.

In further embodiments, the first servo band and the second servo bandare two successive servo bands included in a plurality of servo bands.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment comprisinga tape formatting device that writes servo patterns on a tape for TDScompensation, and the use of the tape in a tape drive, in accordancewith certain embodiments;

FIG. 2 illustrates a block diagram of an exemplary TBS servo pattern, inaccordance with certain embodiments;

FIG. 3 illustrates a block diagram that shows exemplary TBS servopatterns under 0 degree and 30 degrees of rotation, in accordance withcertain embodiments;

FIG. 4 illustrates a block diagram that shows a multi band servo writingmechanism, in accordance with certain embodiments;

FIG. 5 illustrates a block diagram that shows the rotation of a servopattern, in accordance with certain embodiments;

FIG. 6 illustrates a block diagram that shows adjustments made tocompensate for the rotation of a servo pattern, in accordance withcertain embodiments;

FIG. 7 illustrates a block diagram that shows adjustments made forrelative alignment of servo bands, in accordance with certainembodiments;

FIG. 8 illustrates a first flow chart that shows the adjusting of TBSservo patterns for use with TDS compensation, in accordance with certainembodiments;

FIG. 9 illustrates a second flow chart that shows the adjusting of TBSservo patterns for use with TDS compensation, in accordance with certainembodiments; and

FIG. 10 illustrates a block diagram of a system that shows certainelements that may be included in a controller, a tape formatting device,a tape drive, and a computational device as described in FIGS. 1-9 , inaccordance with certain embodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made.

Tape drives may use active skew control to enable read while writeverification that helps to ensure reliability and active TDS control toenable higher track density and hence increased capacity. Both TDS andskew are measured using a pair of servo readers. The two servo readersare positioned at opposite ends of the array of read and writetransducers and read two TBS patterns that bracket each data band duringoperation of the tape drive.

The TBS servo pattern includes groups of stripes written on the magnetictape at an azimuth angle of +α and −α. As the servo reader reads theservo pattern during tape transport, it produces a series of ‘dibit’pulses in response to each stripe, resulting in bursts of dibit pulsesin a repeating 5-5-4-4 pattern. The relative timing of these dibit (alsoreferred to as di-bit) pulses are analyzed by a servo channel to producea series of measurements of the lateral position of the tape relative tothe head referred to as YPOS. The skew of the tape relative to the headis measured by comparing the distance travelled between the arrival of adibit pulse observed with the top servo reader from a given stripe inthe servo pattern and the pulse from the corresponding stripe observedwith the bottom servo reader. This technique is known as top-bottomskew.

TDS is measured by calculating the difference between the YPOS valuemeasured with the top servo reader and YPOS value measured by the bottomservo reader [a value referred to as servo band difference (SBD)]. Anincrease in SBD corresponds to a decrease in the width of the tape.

Changes in the width of the tape that result from changes intemperature, humidity and tension as well as to long term creep effectsare referred to as TDS. Changes in TDS or tape width are measured bychanges in SBD and may be actively compensated. In certain mechanisms,tape tension is used for active TDS compensation. However, this approachis limited in range and introduces additional problems (e.g., longercycle times due to low tension unload, tape cinch, increased risk oftape breakage, variable tape head friction, variable tape head spacing,etc.).

Certain mechanisms may provide a skew-based TDS compensation. In suchmechanism the tape drive is operated with a head that has a nominalrotation angle (beta) relative to the tape, where beta is on the order1-10 degrees. The effective span of the head may then be increased ordecreased by decreasing or increasing the rotation angle. Larger anglesprovide more TDS compensation gain, however as discussed below theyintroduce problems in the performance of the servo channel.

In current tape drives that do not implement skew-based TDScompensation, the absolute value of the angle of the servo stripesrelative to the servo reader is constant. As a result, the dibitsproduced by the servo reader reading stripes with a positive angle isthe same as that from stripes with a negative angle. However, if thehead is rotated clockwise by an angle beta (β) relative to the tape, therelative angle of the servo reader to a first set of stripes will be(α−β) and for the second set of stripes it will be (α+β). For example,for α=12 degrees and β=10 degrees, the relative angles are 2 and 22degrees.

Certain embodiments include operations to rotate the servo pattern (e.g.by rotating servo head during servo formatting, or rotating the positionof the write gaps on the servo format head) by an angle equal to (oralmost equal to) the nominal angle of rotation, beta (β), of the tapedrive head. This solves most of the issues described above but reducesthe useable height of the servo pattern, i.e., the range of YPOS thatcan be measured. To address this, this disclosure provides a set ofrules to adapt the geometry of the servo pattern to increase the rangeof measurement. Finally, certain embodiments provide additionalmodifications to the servo pattern to reduce residual distortions notfully compensated by rotating the servo pattern.

FIG. 1 illustrates a block diagram of a computing environment 100comprising a tape formatting device 102 that writes servo patterns on atape 104 for TDS compensation, and the use of the tape 104 in a tapedrive 106, in accordance with certain embodiments. The tape formattingdevice 102 writes adjusted patterns using a servo write head that hasbeen manufactured as per embodiments provided in this disclosure. Itshould be noted that the adjustments need to be made to the servo writehead during manufacturing of the servo write head. Specifically, theadjustments of the servo write head may need the modifying of thegeometry of the physical write gaps in the servo write head relative tothe write gaps of the servo write head used for writing conventional TBSpatterns. The tape 104 when included in a tape cartridge 108 of the tapedrive 106 is referred to via reference numeral 110.

The tape formatting device 102 writes adjusted servo patterns for TDScompensation on the tape 104, where the servo patterns are written bythe servo write head 112. A controller 116 included in the tapeformatting device 102 controls the movements of the tape 104 and thewriting of servo patterns on the tape 104. The controller 116 of thetape formatting device 102 controls the tape speed and the write currentpulses applied to the servo write head 112 in order to write the servostripes (i.e., the servo pattern). The position of the servo write head112 is fixed during servo formatting.

The tape drive 106 that uses tapes with adjusted servo patterns includesa controller 118 that controls the operations of a servo read head 120,a data read head 122, and a data write head 124. The tape 104 with theadjusted servo patterns is inserted in the tape cartridge 108 of thetape drive 106 and shown via reference numeral 110. The controller 118of the tape drive 106 uses the servo read head 120 to read the adjustedservo patterns written on the tape 110 and then in response to aninput/output (I/O) operation received from a computational device 126,perform read operations from the tape 110 with the data read head 122and write operations from the tape 110 with the data write head 124.

FIG. 2 illustrates a block diagram of an exemplary TBS servo pattern200, in accordance with certain embodiments.

The TBS servo pattern 200 is comprised of groups of stripes written onthe magnetic tape 104. The groups of stripes are referred to as A burst,B burst, C burst, and D burst (as shown via reference numerals 202, 204,206, 208). The TBS servo pattern 200 may be described by the followingparameters: azimuth angle α (shown via reference numerals 210, 212),height b 214 and servo subframe length L 216.

The servo patterns are written at an azimuth angle of +α or −α asillustrated via reference numerals 210, 212 (α=12 degrees in certainembodiments). The azimuth angle, α, in conventional TBS is defined asthe angle perpendicular to the tape travel direction. As the servoreader reads the servo pattern during tape transport, the servo readerproduces a series of dibit pulses in response to each stripe, resultingin bursts of dibit pulses in a repeating 5-5-4-4 pattern where the Aburst 202 and the B burst 204 correspond to the 5-5 pattern and wherethe C burst 206 and the D burst 208 correspond to the 4-4 pattern.Linear tape-open (LTO) format and IBM® Enterprise format specify such5-5-4-4 patterns but other patterns may be used in alternativeembodiments. The relative timing of these dibit pulses are analyzed by aservo channel to produce a series of measurements of the lateralposition of the tape relative to the head referred to as YPOS. The skewof the tape relative to the head is measured by comparing the distancetravelled between the arrival of a dibit pulse observed with the topservo reader from a given stripe in the servo pattern and the pulse fromthe corresponding stripe observed with the bottom servo reader, wherethis technique is referred to as top-bottom skew.

FIG. 3 illustrates a block diagram 300 that shows exemplary TBS servopatterns under 0 degree and 30 degrees of rotation, in accordance withcertain embodiments. Shown in FIG. 3 are readers without rotation (e.g.,reader shown via reference numeral 302) and readers with rotation of 30degrees (e.g. reader shown via reference numeral 308). The rotatedpattern leads to differences in dibit readback signals for A burst vs. Bburst (as shown via reference numeral 304) caused by spatial changeswhere stripes may be closer or further away, and by temporal changes inhead travel over time.

FIG. 4 illustrates a block diagram 400 that shows a multi band servowriting mechanism, in accordance with certain embodiments.

A servo write process 401 is shown in which a servo write head 402writes TBS patterns 404 on a moving tape with a direction of motionshown via reference numeral 407. The first write gap 405 writes thestripes on the A and C burst and the second write gap 406 writes thestripes in the B and D bursts. Write current pulses 408 trigger thewriting of TBS patterns by the write gaps 404, 406. Servo readertrajectory positions may be computed from the distances in the TBSpatterns.

FIG. 4 also shows certain embodiments for multi-band servo patternwriting 412 in which a plurality of servo bands are written on the tapewith a head 414 that writes 5 servo bands (shown via reference numeral416).

FIG. 5 illustrates a block diagram that shows the rotation of a servopattern, in accordance with certain embodiments.

The unmodified servo pattern is shown via reference numeral 502 in thetop servo patterns, and the servo patterns rotated by an angle beta (β)of 10 degrees is shown via reference numerals 504 in the bottom servopatterns.

On rotation, the displacements of the rotated servo patterns from theunmodified servo patterns are shown by the lengths m1 506, m2 508, m3510. The top of the servo stripes in the B 514 and D 518 bursts havedecreased by the length m1 510. The bottom of the servo stripes in the B514 and D 518 bursts have increased by the length m2 508. The bottom ofthe servo stripes in the A 512 and C 516 bursts have decreased by thelength m3 510.

FIG. 6 illustrates a block diagram 600 that shows adjustments made tocompensate for the rotation of servo patterns, in accordance withcertain embodiments.

The rotated servo pattern 504 from FIG. 5 is shown at the top in FIG. 6. The adjusted servo pattern 602 to compensate of the rotations aregenerated by performing the following operations:

(a) The length of the of the top of the servo stripes in the B and Dbursts are increased to increase the height by a distance m1; (referencenumeral 604)

(b) The length of the of the bottom of the servo stripes in the B and Dbursts are decreased to decrease the height by a distance m2; (referencenumeral 606) and

(c) The length of the of the bottom of the servo stripes in the A and Cbursts are increased to increase the height by a distance m3; (referencenumeral 608).

As a result of the operations shown in FIG. 6 , by expanding andtrimming the length of servo stripes, certain effects of rotation arecompensated for, and the adjusted servo bands are shown via referencenumeral 602.

FIG. 7 illustrates a block diagram that shows adjustments made forrelative alignment of servo bands 700, in accordance with certainembodiments. The operations shown in FIG. 7 may be performed by acontroller.

In FIG. 7 two successive servo bands on a tape referred to as servo bandn 702 and servo band n+1 704 are shown. For example, if there are twoservo bands then servo band n is the top servo band and servo band n+1is the bottom servo band on the tape. If there are three servo bandsfrom top to bottom on a tape that are referred to as a first, second,and a third servo band, then servo bands n and n+1 may be the first andsecond servo band respectively, or the second and third servo bandrespectively.

On rotation, the corresponding servo frames of two consecutive have anangular displacement of β′ (shown by reference numeral 706) that needsto be adjusted for to compensate for the effects of rotations. Thecorresponding frames may also be referred to as equivalent frames. Incertain embodiments, the angular displacement is compensated for byshifting servo bands.

FIG. 8 illustrates a first flow chart that shows the adjusting of TBSservo patterns for use with TDS compensation, in accordance with certainembodiments.

Control starts at block 802, in which rotation of timing-based servo(TBS) patterns of two successive servo bands comprising a first servoband and a second servo band take place. The two successive servo bandsmay be included in a plurality of servo bands. From block 802 controlproceeds to block 804 where in response to the rotation of timing-basedservo (TBS) patterns of the two successive servo bands comprising afirst servo band and a second servo band, heights of top and bottomportions of servo stripes of servo frames of the TBS patterns areadjusted to compensate for changes in a usable height of the servostripes caused by the rotation (as shown in FIG. 6 ).

From block 804 control proceeds to block 806 in which the TBS patternsare adjusted to compensate for an angular displacement betweenequivalent servo frames of the first servo band and the second servoband (as shown in FIG. 7 ).

It should be noted that the adjustments made via operations shown inFIG. 8 may be performed by many different embodiments

FIG. 9 illustrates a second flow chart that shows the adjusting of TBSservo patterns for use with TDS compensation, in accordance with certainembodiments It should be noted that the operations shown in FIG. 9 arecertain embodiments for implementing operations shown in FIG. 8 andalternative embodiments may be used.

In certain embodiments, a TBS pattern is described by the followingparameters: azimuth angle α, height b and servo subframe length L, to beused in conjunction with a tape drive where the head has a nominalrotation angle of β (relative to the direction perpendicular to tapetransport in the plane of the tape). Typical values of β are in therange of 2 to 17 degrees.

The TBS pattern is modified by operations shown in blocks 902, 904, 906of FIG. 9 for clockwise rotation. Corresponding modifications may bemade in certain embodiments for counterclockwise rotations.

Control starts at block 902 in which a process rotates the servo patternby an angle (e.g. by rotating the format head by an angle beta duringservo formatting, or by rotating the write gaps on the servo formathead).

From block 902 control proceeds to block 904 where the followingoperations are performed:

The servo pattern is further modified as follows (by modifying thegeometry of the write gaps on the format head)

(a) extend the length top of the second write gap/extend the top of theservo stripes in the B and D bursts such that the height is increased bya distance: m1=a sin (β), where a=(L/2)−b*tan(α)

(b) (optional) reduce the length of the bottom of the second writegap/reduce the length of the bottom of the B and D bursts by a distance:m2=a sin(β)+(b/cos(α))*cos(α−β)−b cos(β) or if the head pitch isexpanded to compensate for the rotation angle β, then: m2=asin(β)+(b/cos(α))*cos(α−β)−b(c) extend the length of the bottom of the first write gap/extend thelength of the bottom of the servo stripes in the A and C bursts by adistance: m3=b cos(β)−(b/cos(α))*cos(α+β) or if the head pitch isexpanded to compensate for the rotation angle β, then:m3=b−(b/cos(α))*cos(α+β).(3) Modify the width of the servo stripes (by modifying the width of thewrite gaps in the servo writer) as follows:(a) Increase the width (measured in the direction of tape travel afterrotation) of servo stripes in the B and D bursts by a factorf1=cos(α−β)/cos(α+β)or(b) Decrease the width (measured in the direction of tape travel afterrotation) of servo stripes in the A and C bursts by a factorf1=cos(α+β)/cos(α−β)or, preferably:(c) Increase the width (measured in the direction of tape travel afterrotation) of servo stripes in the B and D bursts by a factorf3=0.5*(cos(α−β)/cos(α+β)−1)+1 And decrease the width (measured in thedirection of tape travel after rotation) of servo stripes in the A and Cbursts by a factor f4=1−0.5*(1−cos(α+β)/cos(α−β)) For example, for aservo pattern with α=12° and head rotation angle of β=10°f1=1.078,f2=0.928, f3=1.039, f4=0.964.

From block 904 control proceeds to block 906 in which the followingoperations are performed:

Modify the width of the servo stripes (by modifying the width of thewrite gaps in the servo writer) as follows:

(a) Increase the width (measured in the direction of tape travel afterrotation) of servo stripes in the B and D bursts by a factorf1=cos(α−β)/cos(α+β)

or

(b) Decrease the width (measured in the direction of tape travel afterrotation) of servo stripes in the A and C bursts by a factorf1=cos(α+β)/cos(α−β),

or preferably:

(c) Increase the width (measured in the direction of tape travel afterrotation) of servo stripes in the B and D bursts by a factorf3=0.5*(cos(α−β)/cos(α+β)−1)+1 and decrease the width (measured in thedirection of tape travel after rotation) of servo stripes in the A and Cbursts by a factor f4=1−0.5*(1−cos(α+β)/cos(α−β))

For example, for a servo pattern with α=12° and head rotation angle ofβ=10°f1=1.078, f2=0.928, f3=1.039, f4=0.964.

Therefore, certain embodiments shown in FIGS. 1-9 provide mechanisms formaintaining tape dimensional stability and improves the performance of atape based storage system by compensating for rotations of TBS patterns.Such embodiments improve the operations of a tape formatting device, anda computer system by providing mechanisms that improve data storagemechanisms such as a tape drive associated with a computer system.

Additional Embodiment Details

The described operations may be implemented as a method, apparatus orcomputer program product using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. Accordingly, aspects of the embodiments may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,aspects of the embodiments may take the form of a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentembodiments.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present embodiments may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present embodiments.

Aspects of the present embodiments are described herein with referenceto flowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instruction.

FIG. 10 illustrates a block diagram of a system that shows certainelements that may be included in the controller 116, 118, tapeformatting device 102, tape drive 106, or a computational device 126 inaccordance with certain embodiments. The system 1000 may include acircuitry 1002 that may in certain embodiments include at least aprocessor 1004. The system 1000 may also include a memory 1006 (e.g., avolatile memory device), and storage 1008. The storage 1008 may includea non-volatile memory device (e.g., EEPROM, ROM, PROM, flash, firmware,programmable logic, etc.), magnetic disk drive, optical disk drive, tapedrive, etc. The storage 1008 may comprise an internal storage device, anattached storage device and/or a network accessible storage device. Thesystem 1000 may include a program logic 1010 including code 1012 thatmay be loaded into the memory 1006 and executed by the processor 1004 orcircuitry 1002. In certain embodiments, the program logic 1010 includingcode 1012 may be stored in the storage 1008. In certain otherembodiments, the program logic 1010 may be implemented in the circuitry1002. One or more of the components in the system 1000 may communicatevia a bus or via other coupling or connection 1014. Therefore, whileFIG. 10 shows the program logic 1010 separately from the other elements,the program logic 1010 may be implemented in the memory 1006 and/or thecircuitry 1002.

Certain embodiments may be directed to a method for deploying computinginstruction by a person or automated processing integratingcomputer-readable code into a computing system, wherein the code incombination with the computing system is enabled to perform theoperations of the described embodiments.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

At least certain operations that may have been illustrated in thefigures show certain events occurring in a certain order. In alternativeembodiments, certain operations may be performed in a different order,modified or removed. Moreover, steps may be added to the above describedlogic and still conform to the described embodiments. Further,operations described herein may occur sequentially or certain operationsmay be processed in parallel. Yet further, operations may be performedby a single processing unit or by distributed processing units.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter the invention, the inventionresides in the claims hereinafter appended.

*IBM is a trademark of International Business Machines Corporationregistered in many jurisdictions worldwide.

What is claimed is:
 1. A method for a magnetic tape system, the methodcomprising: performing tape dimensional stability (TDS) compensation by:performing a rotation of timing-based servo (TBS) patterns of a firstservo band and a second servo band; and in response to the rotation ofthe TBS patterns of the first servo band and the second servo band,adjusting heights of top and bottom portions of servo stripes of servoframes of the TBS patterns to compensate for changes in a usable heightof the servo stripes caused by the rotation, wherein an entire TBSpattern is comprised of a first pattern and a second pattern, wherein aheight of a top portion of servo stripes of the second pattern isadjusted by a first distance that is a first function of an azimuthangle and an angle of rotation, and wherein a height of a bottom portionof servo stripes of the first pattern is adjusted by a second distancethat is a second function of the azimuth angle and the angle ofrotation.
 2. The method of claim 1, the method further comprising:adjusting the TBS patterns to compensate for an angular displacementbetween equivalent servo frames of the first servo band and the secondservo band.
 3. The method of claim 2, wherein first servo band and thesecond servo band are two successive servo bands included in a pluralityof servo bands.
 4. The method of claim 2, wherein the entire TBS patternis comprised of: the first pattern including servo stripes written on amagnetic tape at an azimuth angle of +α; and the second patternincluding servo stripes written on the magnetic tape at an azimuth angleof −α, wherein the entire TBS pattern has an overall TBS pattern heightof b and a servo sub-frame length of L, wherein the entire TBS patternincluding the first pattern and the second pattern has a rotation angleof β relative to the magnetic tape, and wherein β ranges from 2 degreesto 17 degrees.
 5. The method of claim 4, wherein the height of the topportion of the servo stripes of the second pattern is increased by adistance m1 which is computed as:m1=a sin(β), where a=(L/2)−b*tan(α).
 6. The method of claim 4, whereinthe height of the bottom portion of the servo stripes of the firstpattern is increased by a distance m3, wherein m3 is computed as one of:m3=b cos(β)−(b/cos(α))*cos(α+β); andm3=b−(b/cos(α))*cos(α+β).
 7. The method of claim 2, wherein the entireTBS pattern is comprised of a first TBS pattern associated with a firstservo band n, and a second TBS pattern associated with a second servoband n+1, each of the first and second TBS patterns including a firstsub pattern including a plurality of servo stripes written on a magnetictape at an azimuth angle of +α, a second sub pattern including aplurality of servo stripes written on the magnetic tape at an azimuthangle of −α, each of the first and second TBS patterns including thefirst and second sub patterns having an overall TBS pattern height of band a servo sub-frame length of L, wherein the entire TBS patternincluding the first and second TBS patterns have a rotation angle of βrelative to the magnetic tape, where β ranges of 2-17 degrees, andwherein there is an angle β′ between equivalent frames in the first andsecond TBS patterns relative to the magnetic tape, where β′ is expressedas: β′=β+/−2°.
 8. The method of claim 2, wherein the entire TBS patternis comprised of: the first pattern including a plurality of servostripes written on a magnetic tape at an azimuth angle of α1, and thesecond pattern including a plurality of servo stripes written on amagnetic tape at an azimuth angle of α2, the entire TBS patternincluding the first and second patterns having an overall TBS patternheight of b and a servo sub-frame length of L, wherein the first patternhas an azimuth angle of +α, and the second pattern has an azimuth angleof +−α, and wherein α1≠α2.
 9. A tape formatting device, the tapeformatting device comprising: a controller; and a servo write headcoupled to the controller and configured to write timing-based servo(TBS) patterns on a tape, wherein adjustments to the TBS patterns havebeen made during manufacturing of the servo write head via operationscomprising: performing tape dimensional stability (TDS) compensation by:performing a rotation of the TBS patterns of a first servo band and asecond servo band; and in response to the rotation of the TBS patternsof the first servo band and the second servo band, adjusting heights oftop and bottom portions of servo stripes of servo frames of the TBSpatterns to compensate for changes in a usable height of the servostripes caused by the rotation, wherein an entire TBS pattern iscomprised of a first pattern and a second pattern, wherein a height of atop portion of servo stripes of the second pattern is adjusted by afirst distance that is a first function of an azimuth angle and an angleof rotation, and wherein a height of a bottom portion of servo stripesof the first pattern is adjusted by a second distance that is a secondfunction of the azimuth angle and the angle of rotation.
 10. The tapeformatting device of claim 9, wherein the TBS patterns have beenadjusted during the manufacturing of the servo write head via additionaloperations comprising: adjusting the TBS patterns to compensate for anangular displacement between equivalent servo frames of the first servoband and the second servo band.
 11. The tape formatting device of claim10, wherein first servo band and the second servo band are twosuccessive servo bands included in a plurality of servo bands.
 12. Thetape formatting device of claim 10, wherein an entire TBS pattern iscomprised of: the first pattern including servo stripes written on amagnetic tape at an azimuth angle of +α; and the second patternincluding servo stripes written on the magnetic tape at an azimuth angleof −α, wherein the entire TBS pattern has an overall TBS pattern heightof b and a servo sub-frame length of L, wherein the entire TBS patternincluding the first pattern and the second pattern has a rotation angleof β relative to the magnetic tape, and wherein β ranges from 2 degreesto 17 degrees.
 13. The tape formatting device of claim 12, wherein theheight of the top portion of the servo stripes of the second pattern isincreased by a distance m1 which is computed as:m1=a sin(β), where a=(L/2)−b*tan(α).
 14. The tape formatting device ofclaim 13, wherein the height of the bottom portion of the servo stripesof the second pattern is decreased by a distance m2, wherein m2 iscomputed as one of:m2=a sin(β)+(b/cos(α))*cos(α−β)−b cos(β); andm2=a sin(β)+(b/cos(α))*cos(α−β)−b.
 15. The tape formatting device ofclaim 12, wherein the height of the bottom portion of the servo stripesof the first pattern is increased by a distance m3, wherein m3 iscomputed as one of:m3=b cos(β)−(b/cos(α))*cos(α+β); andm3=b−(b/cos(α))*cos(α+β).
 16. The tape formatting device of claim 12,wherein: the height of the top portion of the servo stripes of thesecond pattern is increased by a distance m1 which is computed as m1=asin (β), wherein a=(L/2)−b*tan(α); the height of the bottom portion ofthe servo stripes of the second pattern is decreased by a distance m2which is computed as one of:m2=a sin(β)+(b/cos(α))*cos(α−β)−b cos(β); andm2=a sin(β)+(b/cos(α))*cos(α−β)−b, and wherein: the height of the bottomportion of the servo stripes of the first pattern is increased by adistance m3 which is computed as one of:m3=b cos(β)−(b/cos(α))*cos(α+β); andm3=b−(b/cos(α))*cos(α+β).
 17. The tape formatting device of claim 10,wherein the entire TBS pattern is comprised of a first TBS patternassociated with a first servo band n, and a second TBS patternassociated with a second servo band n+1, each of the first and secondTBS patterns including a first sub pattern including a plurality ofservo stripes written on a magnetic tape at an azimuth angle of +α, asecond sub pattern including a plurality of servo stripes written on themagnetic tape at an azimuth angle of −α, each of the first and second TBS patterns including the first and second sub patterns having an overallTBS pattern height of b and a servo sub-frame length of L, wherein theentire TBS pattern including the first and second TBS patterns have arotation angle of β relative to the magnetic tape, where β ranges of2-17 degrees, and wherein there is an angle β′ between equivalent framesin the first and second TBS patterns relative to the magnetic tape,where β′ is expressed as: β′=β+/−2°.
 18. The tape formatting device ofclaim 10, wherein the entire TBS pattern is comprised of: the firstpattern including a plurality of servo stripes written on a magnetictape at an azimuth angle of α1, and the second pattern including aplurality of servo stripes written on a magnetic tape at an azimuthangle of α2, the entire TBS pattern including the first and secondpatterns having an overall TBS pattern height of b and a servo sub-framelength of L, wherein the first pattern has an azimuth angle of +α, andthe second pattern has an azimuth angle of +−α relative to the firstpattern, and wherein α1≠α2.
 19. The tape formatting device of claim 18,wherein the entire TBS pattern including the first and second patternshas a rotation angle of β, where β ranges of 2-17 degrees, and whereinα1=α+β, α2=−α+β.
 20. A computer program product, the computer programproduct comprising a computer readable storage medium having computerreadable program code embodied therewith, the computer readable programcode configured to perform operations in a device, the operationscomprising: performing tape dimensional stability (TDS) compensation by:performing a rotation of timing-based servo (TBS) patterns of a firstservo band and a second servo band; and in response to the rotation ofthe TBS patterns of the first servo band and the second servo band,adjusting heights of top and bottom portions of servo stripes of servoframes of the TBS patterns to compensate for changes in a usable heightof the servo stripes caused by the rotation, wherein an entire TBSpattern is comprised of a first pattern and a second pattern, wherein aheight of a top portion of servo stripes of the second pattern isadjusted by a first distance that is a first function of an azimuthangle and an angle of rotation, and wherein a height of a bottom portionof servo stripes of the first pattern is adjusted by a second distancethat is a second function of the azimuth angle and the angle ofrotation.
 21. The computer program product of claim 20, wherein the TBSpatterns are adjusted to compensate for an angular displacement betweenequivalent servo frames of the first servo band and the second servoband.
 22. A method of manufacturing a tape, the method comprising:writing a plurality of servo bands on a magnetic medium by a servo writehead, wherein servo patterns have been adjusted during manufacturing ofthe servo write head via operations comprising: performing tapedimensional stability (TDS) compensation by: performing a rotation oftiming-based servo (TBS) patterns of a first servo band and a secondservo band; and in response to the rotation of the TBS patterns of thefirst servo band and the second servo band, adjusting heights of top andbottom portions of servo stripes of servo frames of the TBS patterns tocompensate for changes in a usable height of the servo stripes caused bythe rotation, wherein an entire TBS pattern is comprised of a firstpattern and a second pattern, wherein a height of a top portion of servostripes of the second pattern is adjusted by a first distance that is afirst function of an azimuth angle and an angle of rotation, and whereina height of a bottom portion of servo stripes of the first pattern isadjusted by a second distance that is a second function of the azimuthangle and the angle of rotation.
 23. The method of manufacturing thetape of claim 22, wherein the TBS patterns are adjusted to compensatefor an angular displacement between equivalent servo frames of the firstservo band and the second servo band.
 24. A method for a servo writehead, the method comprising: configuring the servo write head to writetiming-based servo (TBS) patterns on a tape, wherein adjustments to theTBS patterns have been made during manufacturing of the servo write headvia operations comprising: performing a rotation of timing-based servo(TBS) patterns of a first servo band and a second servo band; and inresponse to the rotation of the TBS patterns of the first servo band andthe second servo band, adjusting heights of top and bottom portions ofservo stripes of servo frames of the TBS patterns to compensate forchanges in a usable height of the servo stripes caused by the rotation,wherein an entire TBS pattern is comprised of a first pattern and asecond pattern, wherein a height of a top portion of servo stripes ofthe second pattern is adjusted by a first distance that is a firstfunction of an azimuth angle and an angle of rotation, and wherein aheight of a bottom portion of servo stripes of the first pattern isadjusted by a second distance that is a second function of the azimuthangle and the angle of rotation.
 25. The method of claim 24, wherein theTBS patterns are adjusted to compensate for an angular displacementbetween equivalent servo frames of the first servo band and the secondservo band.